the heads mount to the block. the manifold bolts onto the heads which are at a different angle ( either the actual head or the hole for the bolts are?).

you will see it. edelbrock has a line of them made just for the vortec heads.

 

alright so lemme see if i got this straight, lets say i get a pair of vortec heads, but in order to mount them on my car i need to get a new intake. and i've been lookin around... most of the vortec heads are for 350s... will those bolt up to my 305?

 

They will bolt up with the vortec specific manifold as I said before the question is will you have interferance problems with the smaller cylinder bore, will the valves be shrouded by the smaller bore? The other thing that will happen is you will drop cylinder compression I think if I remember correctly your cylinder heads are 58cc the vortecs are 64cc. In my opinion I dont think it is worth it if I was going to change heads I would look toward the aftermarket for something 305 specific and also my guess on price for the vortec swap which includes a mild rework of the vortec head, vortec manifold buying a decent carb and the other stuff is bear bones $1000 doing it with new stuff around $2000. I would just put a 50 shot of nitrous on it you will probably make more peak HP.